1. Field of the Invention
The invention relates to a transflexion probe for carrying out a transflexion measurement on a liquid located in a vessel, comprising a probe shaft which is provided with a light guide path in its interior and at whose front end there is arranged an open flow chamber with a reflective plate opposite the front end face of the probe shaft. The invention further relates to a transflective sensor comprising a transflexion probe of the afore-named type and a sensor module coupled thereto.
2. Description of the Related Art
Transflexion probes and transflective sensors are known from Tosi, S. et al.: “Assessment of In-line Near-Infrared Spectroscopy for Continuous Monitoring of Fermentation Processes”, Biotechnol. Prog. 2003, 19, 1816-1821. This printed publication describes a sensor based on spectroscopic measurements in the near infrared region for the purpose of monitoring a culture liquid in a bioreactor. The sensor is assembled from a spectrometer unit and a probe which is inserted into the wall of the bioreactor in a way penetrating the latter, makes direct contact at its front end with the culture broth to be monitored, and is coupled at its rear end to the spectrometer unit. The probe comprises an ordered optical fiber bundle which comprises two groups of light guides, specifically a set of annularly arranged, outer illumination fibers, and a set of central detection fibers arranged in the interior of the ring of illumination fibers. A mirrored reflective plate is arranged at an adjustable distance opposite the front end face of said fiber bundle. The mechanical connection between the end face of the fiber bundle and the reflective plate has lateral openings such that the culture broth into which the probe dips with its front end can flow through the interspace between the reflective plate and the end face of the fiber bundle. Said throughflow is promoted by a separate stirring mechanism for circulating the culture broth. At its rear end, the probe is connected via a flexible optical fiber connection to an NIR spectrometer unit. The spectrometer unit comprises a light source whose light is fed into the input of the illumination fibers. Furthermore the spectrometer unit comprises a spectrometer designed for the near infrared region and whose input arrangement is optically coupled to the output of the detection fibers. Light of the light source is fed into the illumination fibers in order to carry out a measurement. Said light emerges at the front end of the optical fiber bundle and radiates through the flow chamber. On the path through the culture broth in the flow chamber, the illuminating light is subject to scattering and/or absorption in accordance with the optical properties of the culture broth. It is reflected at the opposite end of the flow chamber by the reflective plate and once again traverses the flow chamber to impinge again as detecting light on the end face of the fiber bundle. Said component of the detecting light, which impinges within the acceptance angle of the detection fibers, is led back by the latter to the spectrometer unit and coupled via the input arrangement of the spectrometer into the latter such that it is possible to carry out a spectrometric analysis in a known way.
The low measurement sensitivity owing to high optical losses is a disadvantage in the case of the known instrument. In particular, none of the detecting light which impinges on the end face of the fiber bundle outside the small acceptance angle of the detection fibers can be used for measurement. Also, it is particularly the case that the near infrared region is a spectral region of electromagnetic waves which it is difficult to transmit by means of optical fibers. Here, high losses in the fiber material and, in particular, in bends of the fibers occur. Nevertheless, to achieve a sensitive measurement, the light source must be of correspondingly stronger design so as to compensate the losses. However, this leads to an increased energy consumption and to thermal problems in the spectrometer unit.
It is the object of the present invention to develop a transflexion probe and a transflective sensor of the known type in such a way that it is possible to achieve a high sensitivity even with low light output.